Spectrophotometers quantitatively measure the light reflection or transmission properties of a material as a function of wavelength. UV-VIS spectrophotometers, which utilize light in the ultraviolet WV) and visible (VIS) regions of the electromagnetic spectrum, are commonly used to detect and identify analytes in liquid samples. For example, UV-VIS spectrophotometers may be included as detectors in liquid chromatography systems, such as high-performance liquid chromatography (HPLC), two-dimensional chromatography, ion chromatography, and ultra-high pressure liquid chromatography (UHPLC) systems. An HPLC system may use one or more pumps to flow a pressurized liquid solvent (also termed “mobile phase”) containing a sample mixture through a column filled with a solid adsorbent material (also termed “solid phase”). Each component (e.g., analyte) in the sample mixture interacts with mobile phase and the solid phase differently based on their chemical compositions and structures; components with a higher affinity for the mobile phase will flow through the column more quickly, whereas components with a higher affinity for the solid phase will flow through the column more slowly. The different flow rates of the different components enable components of a complex mixture to be purified, for example. In another example, a specific component may be identified based on an amount of time it remains on the column (e.g., retention time). After each component is eluted from the column, the respective component may flow through the detector (e.g., UV-VIS spectrophotometer).
However, the inventors herein have recognized issues with the above configurations. In order to accurately determine the amount of light absorbed by a sample, stray light as well as light intensity fluctuations are accounted for via a reference signal obtained by a reference detector. In the above configurations, a beamsplitter is typically present to divert a portion of the light emitted by the light source to a reference detector. However, such a configuration increases the optical train of the system, increasing cost and size of the system. Further, diverting a portion of the light beam away from the sample may reduce sample absorbance measurement sensitivity.
The inventors herein have recognized the above-mentioned issues and have engineered a way to at least partially address them. In one example, the issues described above may be addressed by a system including a first light source, a signal detector, a flow path positioned intermediate the first light source and the signal detector, a second light source, and a reference detector. The first light source, the signal detector, and the flow path are aligned along a first axis, and the second light source and the reference detector are aligned along a second axis, different than the first axis. In this way, a second light source may be provided as a reference light source, thus allowing substantially all of the light from the primary light source to be directed to the sample. Further, reliance on a beamsplitter may be reduced or eliminated, at least for the purposes of providing a reference light source. The first light source and second light source may be electrically coupled in series, be cooled by the same thermal control device, and/or otherwise be matched so that intensity fluctuations experienced by the first light source are also experienced by the second light source.
The above advantages and other advantages, and features of the present description will be readily apparent from the following detailed description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.